Peter G. Bullough

THE STRENGTH OF THE MENISCI OF THE KNEE AS IT RELATES TO THEIR FINE STRUCTURE

1. The orientation of collagen fibres of the menisci of the knee has been demonstrated by polarised light microscopy. 2. As might be supposed from its fibre structure, the ultimate tensile strength of the meniscal tissue is dependent upon the axis of loading. 3. The tensile strength of the meniscus is similar to that of articular cartilage.

Spontaneous osteonecrosis of the knee : The result of Subchondral Insufficiency Fracture

Background: Spontaneous osteonecrosis of the knee is a superficial subchondral lesion classically seen in the medial femoral condyle; in general, it is markedly different in its clinicopathological presentation from the classic wedge-shaped subchondral osteonecrotic lesions seen in the hip, knee, and other joints. Recent reports on subchondral insufficiency fracture of the femoral head, which has marked morphological similarities with spontaneous osteonecrosis of the knee, led us to reevaluate a series of patients who had had operative treatment because of a clinical and pathological diagnosis of spontaneous osteonecrosis of the knee. Methods: We reviewed the cases of fourteen patients who had had operative treatment of spontaneous osteonecrosis of the knee in order to reevaluate the gross and histological morphology of this lesion. The patients included eight women and six men who ranged in age from fifty-nine to eighty-eight years. In all patients, the diagnosis of spontaneous osteonecrosis of the knee had been based on clinical presentation, imaging studies, and pathological findings. The appearance of the lesion on plain radiographs was categorized into four stages, which corresponded to the gross and histological findings. In stage 1, the radiographic appearance is normal; in stage 2, a radiolucent oval area is seen subchondrally or there is slight flattening of the convexity of the condyle, or both; in stage 3, the radiolucent area is expanded and is surrounded by a sclerotic halo; and in stage 4, secondary osteoarthritic changes are apparent. Results: No patient had a stage-1 lesion. Three patients, all of whom had a stage-2 lesion, were considered to have a subchondral insufficiency fracture of the medial femoral condyle. Another six patients, all of whom had a stage-3 lesion, were considered to have a subchondral fracture and associated focal osteonecrosis that was confined to the area between the fracture line and the articular surface. The remaining five patients, three of whom had a stage-3 lesion and two of whom had a stage-4 lesion, had indeterminate findings because the lesion had become detached from the condyle. Conclusions: Our histopathological findings suggest that the primary event leading to spontaneous osteonecrosis of the knee is a subchondral insufficiency fracture and that the localized osteonecrosis seen in association with this disease is the result of a fracture.

THE DISTRIBUTION OF COLLAGEN IN HUMAN ARTICULAR CARTILAGE WITH SOME OF ITS PHYSIOLOGICAL IMPLICATIONS

1. Serial slices of articular cartilage obtained at necropsy from apparently normal femoral condyles of individuals between the ages of twenty-six and sixty were examined chemically, by electron microscopy and for permeability. 2. The most superficial layer was shown by chemical analysis and electron microscopy to have the highest collagen content, which fell sharply with distance from the articular surface. On the other hand the glycosaminoglycan content was very low in the superficial layers but increased with depth. This variation was found in all specimens tested but the absolute levels of collagen and of glycosaminoglycans were widely different. There was no correlation of chemical composition with age. 3. Collagen fibrils in the superficial layer were of much smaller diameter than in the deeper zones. 4. Hydraulic permeability was shown to depend more on glycosaminoglycan than on collagen content, although it varied inversely with both these factors. 5. The results obtained demonstrate clearly the close relation between the physical properties of cartilage and its chemical composition.

THE SIGNIFICANCE OF THE FINE STRUCTURE OF ARTICULAR CARTILAGE

The collagen framework of articular cartilage is disposed, as in other connective tissues, to resist tension forces within the material. In this paper the fine structure of articular cartilage, as demonstrated by polarised light microscopy and electron microscopy, is related to the gross anatomy and to the naked eye changes of chondromalacia and fibrillation.

THE RELATIONSHIP BETWEEN DEGENERATIVE CHANGES AND LOAD-BEARING IN THE HUMAN HIP

1. A predictable pattern of degeneration occurs on both the femoral head and the acetabulum and this pattern is age dependent. 2. The degenerative areas on the femoral head are related to habitual non-use. 3. The hip is shown to be anatomically incongruent, and the dome of the acetabulum, a predictable area of degeneration, is shown also to be an area of habitual non-use. 4. The possible relationships between age-dependent degenerative changes and senile degenerative joint disease is discussed and the importance of changing geometry stressed.

Size of metallic and polyethylene debris particles in failed cemented total hip replacements

Reports of differing failure rates of total hip prostheses made of various metals prompted us to measure the size of metallic and polyethylene particulate debris around failed cemented arthroplasties. We used an isolation method, in which metallic debris was extracted from the tissues, and a non-isolation method of routine preparation for light and electron microscopy. Specimens were taken from 30 cases in which the femoral component was of titanium alloy (10), cobalt-chrome alloy (10), or stainless steel (10). The mean size of metallic particles with the isolation method was 0.8 to 1.0 microns by 1.5 to 1.8 microns. The non-isolation method gave a significantly smaller mean size of 0.3 to 0.4 microns by 0.6 to 0.7 microns. For each technique the particle sizes of the three metals were similar. The mean size of polyethylene particles was 2 to 4 microns by 8 to 13 microns. They were larger in tissue retrieved from failed titanium-alloy implants than from cobalt-chrome and stainless-steel implants. Our results suggest that factors other than the size of the metal particles, such as the constituents of the alloy, and the amount and speed of generation of debris, may be more important in the failure of hip replacements.

Malignant Fibrous Histiocytoma and Osteosarcoma in Association with Bone Infarcts

Four patients, two of them former caisson workers, had malignant tumors of bone associated with bone infarcts in the femur. One of the tumors was osteogenic sarcoma and the other three were malignant fibrous histiocytomas. Despite amputation and other treatment, only one patient survived.

Subchondral insufficiency fracture of the femoral head: histopathologic correlation with MRI

Abstract Objective. To correlate the magnetic resonance imaging (MRI) features with the histopathologic findings in subchondral insufficiency fracture (SIF) of the femoral head. Design and patients. This study was based on a retrospective review of the MRI features and histopathologic findings in seven patients with SIF who had had total hip replacement. Results. In all seven cases, MRI showed a bone marrow edema pattern in the femoral head, and a focal low-intensity band beneath the articular cartilage on some slices (not all) on the T1-weighted images. The shape of the low-intensity band varied: it was irregular and serpentine in four cases, well-delineated, smooth, and a mirror image to the articular surface in two cases, and parallel to the articular surface in one case. On histologic examination, the low-intensity band on MRI corresponded to a fracture line and its associated repair tissue. In all but one case, the band was not visible on T2-weighted or fat suppression images, and the proximal subchondral portion of the lesion had a homogeneous high signal intensity. This region of high signal intensity corresponded histopathologically to viable bone and marrow tissue with associated callus, edema, and vascular granulation tissue. Conclusions. SIF of the femoral head characteristically demonstrates a low-intensity band on T1-weighted images that corresponds, histopathologically, to a linear subchondral fracture and its associated repair tissue. In most cases, the subchondral portion of the lesion appears on T2-weighted images as an area of homogeneously high signal intensity.

Total Hip Replacement Failures: A Histological Evaluation

The first twenty failed total hip replacements in one hospital population showed infection in twelve (two Charnley and ten McKee-Farrar) and loosening in eight (McKee-Farrar). Acute inflammation was present in all of the infections and ranged from mild to severe. Chronic inflammation was universally seen, more severe in the presence of infection. Intracellular and extracellular metallic debris was seen in all but two cases. Acrylic debris was found extracellularly in all cases and intracellularly in small amounts in three. Debris resembling polyethylene was seen in two patients. It was not possible to determine what part the debris played in inflammation versus infection.

The morphology of the calcification front in articular cartilage. Its significance in joint function

Biochemical and histochemical studies have indicated that there is specific cellular activity in the region of the calcification front of articular cartilage implying that a regulation process takes place there. Using scanning and transmission electron microscopy and light microscopy to examine tissue sections of both undecalcified and decalcified articular cartilage in the region of the calcification front, we have looked at its morphology with particular reference to its cellular control. Our observations show that physiological calcification is an active process under cellular control and is related to the presence of extracellular membrane-bound matrix vesicles.